Medical devices may be coated so that the surfaces of such devices have desired properties or effects. For example, it may be useful to coat medical devices to provide for the localized delivery of therapeutic agents to target locations within the body, such as to treat localized disease (e.g., heart disease) or occluded body lumens. Localized drug delivery may avoid some of the problems of systemic drug administration, which may be accompanied by unwanted effects on parts of the body which are not to be treated. Additionally, treatment of the afflicted part of the body may require a high concentration of therapeutic agent that may not be achievable by systemic administration. Localized drug delivery may be achieved, for example, by coating balloon catheters, stents and the like with the therapeutic agent to be locally delivered. The coating on medical devices may provide for controlled release, which may include long-term or sustained release, of a bioactive material.
Aside from facilitating localized drug delivery, medical devices may be coated with materials to provide beneficial surface properties. For example, medical devices are often coated with radiopaque materials to allow for fluoroscopic visualization while placed in the body. It is also useful to coat certain devices to achieve enhanced biocompatibility and to improve surface properties such as lubriciousness.
Metal stents may be coated with a polymeric coating that may contain a dissolved and/or suspended bioactive agent. The bioactive agent and the polymeric coating may be dissolved in a solvent mix and spray coated onto the stents, for example, by gas assist atomized spray coating. The solvent may then evaporate to leave a dry coating on the stent.
Drawbacks to gas assist atomized coating include its low material transfer efficiency and the presentment of polymer and drug to the inside of the device being coated, such as the inside surface of a stent. Another drawback to gas assist atomized coating includes the resulting high degree of shear to the coating solution, which makes the use of shear sensitive coating materials impossible. Webbing may also present a problem, such as webs of the coating between stent struts.
There is therefore a need for alternative coating methods for medical devices.